US 3298907 A
Description (OCR text may contain errors)
United States Patent 3,298,907 NON-FLAMMABLE CARBON DISULFIDE FUMIGANT COMPOSITION Albert W. Bauer and Frederick B. Hill, Jr., Wilmington,
Del., assignors to E. 1. du Pont de Nemours and Company, Wilmington, Del., a corporation of Delaware No Drawing. Filed Jan. 21, 1965, Ser. No. 427,172 2 Claims. (Cl. 167-23) The present invention is directed to improved fumigant compositions containing carbon disulfide.
Carbon disulfide is a known liquid 'fumigant which will eflectively control many types of grain insects. When applied as a liquid the readily volatile carbon disulfide emits fumes which pass downward and permeate the grain with no undesirable vapor Stratification or channeling effect.
Carbon disulfide, however, is flammable and its use in open areas where it becomes mixed with air presents dire fire and explosive hazards.
Modern techniques for overcoming the fire and explosion hazards resulting from the use of carbon disulfide involve mixing the carbon disulfide with such nonflammable, volatile materials as carbon tetrachloride, dichloromethane and 1,2-dibromoethane as described in U.S.P. 2,803,581. However, a substantial proportion (60% to 78% by volume) of the mixture described in U.S.P. 2,803,581is carbon tetrachloride, a material highly toxic to humans which should not be vaporized in an open area if it can avoided. Furthermore, a composition of the type describe-d in U.S.P. 2,803,581, wherein no flash or fire occurs in an open cup, usually contains a relatively small amount, about 13% by volume, of the active fumigant ingredient. Furnigant compositions which are safe, less toxic, and more concentrated in the carbon disulfide fumigant would therefore be advantageous and a signiticant advance in the art.
It is, therefore, an object of this invention to provide an improved fumigant mixture comprising carbon disu fide.
It is another object of this invention to provide a grain fumigmant based on carbon disulfide that is safe from fire "hazards, employs non-toxic fire supressors, has a high content of carbon disulfide, and is azeotropic in character.
These and other objects will become apparent from the following description and claims.
More specifically, the present invention is directed to a fumigant composition comprising from to 40% by weight of carbon disulfide, 'from 15% to 60% by weight of 1,1,Z-trichloro-l,2,2-trifluoroethane and from 25% to 60% by weight of dichloromethane. Compositions within 'these component concentration ranges are non-flammable,
employ non-toxic fire suppressors and consequently are no more toxic than the carbon disulfide renders them, and may contain up to as much as 40% by weight of carbon disulfide.
The compositions of the present invention also provide liquid ttumigants that have a relatively low boiling point and are faster evaporating when applied to grain.
The compositions of the present invention are further characterized by the fact that all compositions within the defined component limits closely resemble an azeotrope in behavior. All the compositions of the present invention have a boiling point in the range between 34.6 C. and 35 C.
An azeotrope is a liquid mixture that exhibits a maximum or minimum boiling point. mixture is that its distillate has the same composition as the original mixture and no change in properties of the mixture or the distillate occurs as a result of evaporation. Actually, within the defined range of compositions of the present invention there exists a true ternary azeotrope.
A feature of such a 3,298,907 Patented Jan. 17, 1967 The composition of this true ternary azeotrope boiling at 34.6 C. at 760 mm. Hg is 21.5% by weight of carbon disulfide, 40.3% by weight of 1,1,2-trichloro-1,2,2-trifluoroethane, and 38.2% by weight of dichloromethane.
Representative examples of the compositions of the present invention having carbon disulfide concentrations from the lower 10% limit to the upper 40% limit are set forth in Table I below. In these compositions each of the other two components, 1,1,2-trichloro-1,2,2-trifluoroethane and dichloromethane, are present in varying amounts within the specified limits in order to add up to a total.
TAB LE I [Amounts are in percent by weight] CS I CFzClCFClz CHzClg Compositions having less than 10% carbon disulfide are operative as non-flammable fumigants of low toxicity, but they exhibit relatively low insecticide activity and have a wider boiling range than the com-positions of the present invention with higher amounts of carbon disulfide. Compositions having appreciably more than 40% of carbon disulfide are flammable and present fire and explosion hazards. Compositions with less than 15% chloro-l,2,2-trifiuoroethane are flammable and/or have higher boiling points and are therefore less azeotropic in behavior than the composiitons of the present invention. Compositions with more than 60% l,1,2-trichloro-1,2,2- trifluoroethane, although non-flammable, are less desirable than the invention compositions because they exhibit higher boiling points. Compositions with more than 60% dichloromethane show this same behavior, whereas those 1,2,2-trifluoroethane and dichloromethane taken in combination with the defined limits provide a range of nonflammable compositions containing up to 40% by weight of carbon disulfide. The properties of the defined compositions were unexpected, since 1,l,2-trichloro-l,2,2-triiluoroetha-ne and dichloromethane taken singly form flammable binary mixtures with carbon disulfide when the carbon disulfide exceeds about 30% of these binary mixtures. Moreover, each of these haloalkanes forms a fiammable binary azeotrope with carbon disulfide having a carbon disulfide content of 38% and 35%, respectively.
In addition to the mixture of 21.5% by weight of carbon disulfide, 40.3% by weight of 1,1,2-trichloro-1,2,2- trifluoroethane, and 38.2% by weight of dichloromethane which forms a true azeotrope boiling at 34.6 C. at 760 mm. Hg pressure and which will not fractionate upon evaporation, mixtures of these three components having compositions within the ranges defined above have boiling points within the range of from 34.6 C. to 35 C. and behave essentially like an azeotrope in undergoing practically no fractionation under the evaporation conditions of use of the fumigant. This property is particularly valuable in fumigant use because compositions over a relatively wide range of component concentrations may be employed without the danger of a fractionation into flammable mixtures. Once evaporation of the fumigant and permeation of the vapors into a granary bin or other space to be treated has occurred, thorough mixing of the gases to insure a uniform, non-flammable composition is impossible. Such a uniform composition is provided, however, by the compositions of this invention since the 1,1,2-trigas composition is essentially uniform throughout evaporation and has the same component concentrations in the gas phase as existed in the original liquid mixture. Unfortunately, non-flammable liquid mixtures of carbon disulfide, carbon tetrachloride, and dichloromethane are not azeotropic in character and hence do not evaporate uniformly. Such liquid mixtures create a fire hazard by preferential evaporation of the flammable binary azeotrope of carbon disulfide and dichloromethane. No ternary azeotrope of carbon disulfide, carbon tetrachloride, and trichloromethane exists, and flammable vapors may be emitted, therefore, from mixtures of these components.
Representative examples of the present invention follow. All parts are by weight unless otherwise specified.
Example 1.-Flash point of fumigant mixtures Tests were made by the open-cup method (ASTM method D-1310-63) for flash point on various compositions of the present invention. The specific compositions employed and the results obtained are set forth in Table II below:
TABLE II Corn osition ereent by Weight) p p Flash Point, C.
CS CF ClCFOl; (DI-I 01 15 25 60 None to the boiling point. 21. 5 40. 3 38. 2 Do. 40 35 25 D0. 40 45 Do. 15 60 D0. 34 56 10 -21. 35 35 30 None to the boiling point. 30 30 D0. 40 4O 20 21 F. 50 25 25 41, accompanied by fire.
From the above it can be seen that fumigant mixtures with 40% and below of carbon disulfide, a dichloromethane content exceeding 25%, and at least 15% of 1,1,2- trichl-oro-l,2,2-trifluoroethane do not present a potential fire hazard.
Example 2.Aze0tr0pic character of fumigant compositions Tests were made to demonstrate the azeotropic character of the compositions of the present invention. The boiling points were first established for various liquid mixtures of carbon disulfide, 1,1,2-trichloro-1,2,2-trifluoroethane, and dichloromethane. Fifty grams of these same mixtures were then allowed to evaporate in an enclosed space with a volume of liters. After approximately of the liquid had evaporated, .samples of the vapors and the remaining liquid mixture were analyzed by vapor-phase chromatography and the percent weight concentration of each component in the respective phase determined. The results obtained, together with the boiling points of the analyzed mixtures, are reported below in Table III? TABLE III.-EVAPO RATION It is evident from the above results that no fractionation occurred in mixture B, the true azeotrope composition, and that only insignificant changes occurred during evaporation in mixtures A and C which are azeotropiclike in behavior. The above results are merely representative. All the compositions within the defined invention possess azeotropic characteristics since they all boil in the range between 34.6 C. and 35 C. and do not fractionate under conditions of evaporation.
Example 3.Kill of insects by fumigant compositions In this example, tests were made to determine the effect, if any, on the insect killing power of the carbon disulfide caused 'by mixing carbon disulfide with the fire suppressors dichloromethane and 1,l,2-trichloro-1,2,2- trifluoroethane. Tests of the fumigant compositions on insects were conducted using the following procedures.
Adult flour beetles, granary weevils and carpet beetles in the larval stage were confined in 500 ml. jars in the presence of varying amounts of fumigant as measured by a micropipette. The fumigant compositions were admitted to the jar on filter paper. The test containers were held at 27 C. for 24 hours and aired. Thereafter, a count of the living and dead insects was made. The counting was done by transferring the insects to a plate maintained at 40 C. and noting as alive those insects which showed motion under 4 magnification.
The maximum dosage of fumigant composition was 10 microliters or 0.01 ml. of liquid carbon disulfide per 500 ml. of space. This dosage corresponded to about 0.6 ml. per cubic foot (0.028 cubic meter) or to about 600 ml. per 1000 cubic feet (28 cubic meters). This amount was much less than the 10 pounds of carbon disulfide (5.7 liters) per 1000 cubic feet recommended for bagged grain in atmospheric vaults (Insect Pests of Stored Grain and Grain Products, Burgess Pub. Co., 1941). Allowance was made for the insects being unprotected and at a higher temperature in the laboratory than those living under actual grain storage conditions. Even with this lower dosage of 10 microliters, 100% kill was attained in the laboratory in each case.
Employing 2O insects in each case, a mixture of 21.2% by weight of carbon disulfide, 39.5% by weight of 1,1,2- trichloro-1,2,2-trifluoroethane, and 39.3% dichloromethane was tested by this procedure for its effectiveness in killing flour and carpet beetles and .granary weevils.
Percent Kill after 24 Hours Exposure Dosage of Fumigant in microliters of carbon disulfide per 500 ml. Flour Carpet Granary Beetle Beetle Weevil When carbon disulfide alone in the same dosages was used, the same percentage kill within experimental error was effected, showing that the additives for eliminating the explosion and fire hazards are inert with respect to O F GRAIN FUMIGANT Mixtures A B 0 Initial B.P., C 34.8 34. 6 34.9
Wt. Percent Evaporated.-. 47 61 54 Components" TTE CS2 CH Cl TTE CS2 OH Cl TTE CS2 CHzClz Original Mixture (Percent) 25.0 40. 0 35. 0 40. 3 21.5 38.2 40. 0 10. 0 50. O Vapor after Evaporation (Percent) 27. 3 36.8 35.9 40. 4 21. 5 38.1 40.1 13. 2 46. 7 Liquid after Evaporation (Percent) 24. 4 39.1 36. 5 40. 4 21.7 37. 9 40. 5 10.0 49. 5
CST-carbon disulfide. CH Clg-dichloromethane.
the insect killing power of the fumigant at the concentrations employed.
As many apparently widely different embodiments of this invention may be made without departing from the spirit and scope thereof, it is to be understood that this invention is not limited to the specific embodiments thereof except as defined in the appended claims.
The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:
1. A furnigant composition consisting essentially of from about to 40% by weight of carbon disulfide, from about to 60% by weight of 1,1,2-trichloro- 6 1,2,2-trifluoroethane, and from about to by weight of dichloromethane.
2. An azeotropic fumigant composition consisting of 21.5% by weight of carbon disulfide, 40.3% by weight of 1,1,2-trichloro-1,2,2-trifiuoroethane, and 38.2% by weight of dichloromet hane, said composition characterized by having a constant boiling temperature of 34.6 C. :at 760 mm. Hg. pressure.
No references cited.
LEWIS GO'ITS, Primary Examiner.
S. K. ROSE, Assistant Examiner.